The auditory sensitivity of the Lemur

Abstract

A single-lever shock avoidance conditioning technique was used to generate auditory behavioral thresholds for Lemur catta over the frequency range 100 Hz to 75 kHz. The results indicate a sensitivity of at least 60 dB below one dyne/cm2 from 1 kHz to 32 kHz and, throughout the entire frequency range, appear to be compatible with other available prosimian data. A contrast between anthropoids and prosimians indicates a loss in high frequency sensitivity for the former group, but a greater sensitivity for lower frequency stimuli. Analysis of lemur vocalizations indicates a preponderance of relatively low frequency components. Descriptions of the conditioning technique, threshold criteria, and procedures of sound measurement are included.As part of a long-term investigation of the hearing of prosimians, we have assessed the auditory capabilities of several species of lemurs by means of conditioning techniques. We chose this representative of the suborder prosimii since no quantitative behavioral data on hearing were available for this animal (Vernon, '67) and the Oregon Regional Primate Research Center maintains one of the largest captive populations of lemurs in the world.In a previous paper (Mitchell, Gillette, Vernon and Herman, '70), we reported on the auditory sensitivity of Lemur catta, L. fulvus, and L. macaco over the frequency range of 100 hertz to 40 kilohertz, using a two-lever positive reinforcement technique patterned after that used by Gourevitch and Hack ('66). The derived data were obtained only after long and exasperating training and testing sessions; we feel this technique is too difficult for the lemur. Further, it did not permit an appropriate degree of stimulus control, resulting in heightened variability and lessened confidence in the data. Accordingly, we adopted a different behavioral technique, similar to the single-lever shock avoidance paradigm reported by Clack and Herman ('63 ), and replicated these threshold determinations, this time considering only the species L. catta. These data (Mitchell, Vernon and Herman, '71) indi- AM. J. PHYS. ANTHROP., 38: 365-370cate an increased sensitivity, relative to the first study, of up to 20 decibels, especially for the mid-range frequencies. Variability of behavior was also considerably lessened. Since differences between species were negligible in the first study, and because we feel the 20 dB difference between the first and second study is attributable to the response contingencies of the two methods, we would accept the data of the second study as being more accurate.The present report (study 3 ) considers the high frequency sensitivity of L. catta from 8 kHz to 75 kHz; to complete the audiogram, we are also presenting the results of study 2, which extended down to a frequency of 100 Hz. METHODThe calibration procedures used in the present study differed from those previously employed; however, the training procedures, threshold testing techniques, and criteria were the same. Although a more complete description of these procedures appear...

What Do Primates Hear? A Meta-analysis of All Known Nonhuman Primate Behavioral Audiograms

“…The final audiogram presented in Gillette et al (1973) for Lemur catta represents the end product of the previous studies by Mitchell (1970), Mitchell et al (1970), andMitchell et al (1971). The only significant methodological differences between Gillette et al (1973) and the Mitchell et al (1971) was that the shock rate and intensity were lower (only intratrial false-positives were punished) and the method used to calibrate the sound pressure levels was changed.…”

“…? Bragg and Dreher 1969 Double-walled soundproof room Noncalibrated Sound-treated room Head position Heffner and Masterson 1970 Double-walled chamber Head position Gourevich 1970 Double-walled chamber Probe tube Mitchell et al 1970 Double-walled chamber Pinna position with dummy animal Mitchell 1970 Double-walled chamber Pinna position with dummy animal Mitchell et al 1971 Double-walled chamber Pinna position with dummy animal Green 1971Green , 1975 Double-walled chamber (40-60 dB) Probe tube Gillette et al 1973 Double-walled chamber Hot-spots Pugh et al 1973 Double-walled chamber Probe tube Stebbins 1973 Double-walled chamber Probe tube Beecher 1974a Double-walled chamber with cotton Head position Beecher 1974a…”

Basicranial morphology and ontogeny of the extinct giant lemur Megaladapis

“…It should be noted that the importance of the stiffness provided by the air volume within the middle ear is not adequately emphasized in classical considerations of middle-ear impedance, which tend, instead, to focus on the reactance provided by the mass of the ossicular system (for an insightful quantitative study of the relationship of stiffness and mass in total middle-ear impedance, see Webster and Webster, 1975). Audiograms of extant lemurs (Gillette et al, 1972) indicate that they possess no special auditory sensitivity at low frequencies. We have no evidence that the giant lemurs were different: the mere fact that their tympanic floors are unexpanded cannot be taken as evidence of unusual hearing adaptations or lifeways not found in the surviving lemur fauna.…”

Primate hearing from a mammalian perspective

“…Only the patas monkey seems unusual with poor sensitivity overall (no thresholds below 10 dB) and much poorer hearing at low frequencies, with no responses obtained below 125 Hz. Although this is possibly a true (Gillette et al, 1973), lesser bushbaby (Galago senegalensis) (Heffner HE et al, 1969b), potto (Perodicticus potto) (Heffner and Masterton, 1970), slow loris (Nycticebus coucang) (Heffner and Masterton, 1970), and tree shrew (Tupaia glis) (Heffner HE et al, 1969a). The human audiogram represented by the gray line is included for comparison.…”